CVE-2026-31446 ext4: fix use-after-free in update_super_work when racing with umount
A use-after-free in the Linux kernel ext4 filesystem allows attackers to cause denial of service or potentially execute code during unmount races.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-31446?
CVE-2026-31446 is a high-severity use after free vulnerability in Linux kernel, published on 22 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ext4: fix use-after-free in update_super_work when racing with umount
Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount filesystem") moved ext4_unregister_sysfs() before flushing s_sb_upd_work to prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups reads during unmount. However, this introduced a use-after-free because update_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which accesses the kobject's kernfs_node after it has been freed by kobject_del() in ext4_unregister_sysfs():
update_super_work ext4_put_super ----------------- -------------- ext4_unregister_sysfs(sb) kobject_del(&sbi->s_kobj) __kobject_del() sysfs_remove_dir() kobj->sd = NULL sysfs_put(sd) kernfs_put() // RCU free ext4_notify_error_sysfs(sbi) sysfs_notify(&sbi->s_kobj) kn = kobj->sd // stale pointer kernfs_get(kn) // UAF on freed kernfs_node ext4_journal_destroy() flush_work(&sbi->s_sb_upd_work)
Instead of reordering the teardown sequence, fix this by making ext4_notify_error_sysfs() detect that sysfs has already been torn down by checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call in that case. A dedicated mutex (s_error_notify_mutex) serializes ext4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs() to prevent TOCTOU races where the kobject could be deleted between the state_in_sysfs check and the sysfs_notify() call.
Weakness: CWE-416
Which versions are affected by CVE-2026-31446?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31446?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-31446 being exploited?
There is no known exploitation of CVE-2026-31446 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-83282, BELL-CVE-2026-31446, DEBIAN-CVE-2026-31446, GHSA-wwvq-j7g5-3qrf, ROOT-OS-DEBIAN-11-CVE-2026-31446, ROOT-OS-DEBIAN-12-CVE-2026-31446 and 4 more.